The invention relates to the cooling of electric devices for starting aeronautical engines.
A particular field of application of the invention is that of aeronautical engines with a gas turbine, in particular turbo-engines.
The starting of an aeronautical engine is conventionally ensured by an electric machine driving a shaft of the engine. The electric machine may be an electric motor or a machine forming a starter/generator (or S/G) operating in a motor mode upon starting and then in a synchronous generator mode.
It is necessary upon starting to remove the calories produced by the electric starting device, i.e. by the actual electric machine and also preferably by the electronic power circuit used for controlling the electric machine, as for example indicated in document EP 1 953 899.
In an aeronautical engine, the fuel is conventionally used as a coolant fluid either directly or by heat exchange with a heat transfer fluid, for example oil.
The fuel is pumped into a tank and brought to a fuel circuit of the engine which comprises a high pressure pump. The latter delivers fuel under a high pressure to a main circuit for feeding the combustion chamber of the engine. The high pressure pump is typically a gear pump driven from a shaft of the engine via a mechanical transmission box or accessory gear box AGB.
It has been proposed to ensure the cooling of an electric starting device by fuel taken at the outlet of the high pressure pump of the pumping circuit of the engine. In order to ensure a sufficient flow of coolant fuel at a low starting speed, it is necessary to give significant capacity to the high pressure pump. Such a capacity is then widely overdimensioned for providing the flow rate required by the main feeding circuit during the operation of the engine at a rated speed, which imposes diversion of a significant portion of the fuel provided by the high pressure pump in order to return it to low pressure. The use of additional pumps mechanically driven by the engine in order to feed the cooling device of the electric starting device may be contemplated. But such a solution is expressed by an increase in mass, by the requirement of an additional mechanical link with the AGB and poses a problem at high speed by diverting then a too large flow of fuel.
In document U.S. Pat. No. 3,733,816, it has been proposed to cool an electronic calculator of a gas turbine engine by means of fuel provided by a pump located upstream from the high pressure fuel pump, in series with the latter, both pumps being mounted on a common driving shaft coupled with the engine.